Bio substrate is not something new, it have been used for frogs and smaller lizards for many years. But there are different ways to do bio substrate. The easy way is just to use some spagnum and add springtails and woodlice. There are also what i will call an advanced bio substrate, it is where you do even more to get as close to nature as possible.

One thing that is needed no matter which bio substrate is used, it is important to make sure it don’t dry out, since it will kill the insects living in it. The depth of the substrate is not that important for its survival, but i do recommend a depth of at least 10-15 cm, that way the iguanas have deep enough substrate to lay eggs in.

The bio substrate i use in my cages, are what i will call the more advanced way. This substrate is made from a mix of forest dirt( from a beech tree forest) and compost dirt( from my own compost, so that i know what it contain), it is important to be sure that there are no pesticides in it.

The bugs living in this substrate are, woodlice, springtails, earth worms, earwigs, milipedes, centipedes and a few snails.

The centipede babies eat small insects, and that include the reptile mites. This is one reason why i added them to my cages, they will not hurt the adult iguanas.

All these other bugs live of dead material, that include the iguanas poop and shed. They also eat food that drop to the bottom of the cages. All in all over time there will be a build up of nutrition in the substrate from all the poop from the insects, one way to solve this without having to change the substrate is to add live plants, but with fiji iguanas it can be a challenge since they will often eat the plants or climb in them until the plants break and die.

Another way is to make a substrate that work so well that this “forest fungus”(not to be confused with normal mold) will start to grow( see pic ), this fungus live of the nutrition that come from the poop from the insects. The iguanas have not showen any interest in the fungus and the fungus have not had any bad effect on the iguanas.

If there grow to much fungus some of it can easy be removed,

Over time the insects will have eaten alot of the leaves and stuff that are in the substrate, then all that need to be done is to add some new compost and forest dirt mix on top of the old.

The soil.

With the combo of forest floor and compost dirt mixed with dead leaves, makesa nice loose substrate. It is important to have a rather loose substrate, so that you dont need to "air" your substrate. A compact soil will need to be loosen up from time to time, so that the bugs can get into the soil and eat the nutrients left by the iguana droppings.

With a loose soil, bugs like small millipedes and woodlice wont have any problems digging into the soil to get to those nutrients.

As for plants, the iguanas eat almost every plant we have tried from hibiscus to cactus. So far the only plants they have shown zero interest in, has been bromeliads. We use the medium size bromeliads in our cages at the moment, but do plan on adding a couple of the big types.

Woodlice taking care of the iguana droppings.

Some type of fungus that sometimes show up in a new setup substrate. It is not harmfull to the iguanas.